The present invention relates to a field-emission electron source having prospective applications to an electron-beam-induced laser, a flat solid display device and a ultra-high-speed extremely small vacuum element. More particularly, it relates to a vacuum-sealed field-emission electron source, for use in a compact flat display device, in which a space formed between a semiconductor substrate and a sealing cover is retained to be vacuated, and a method of manufacturing the vacuum-sealed field-emission electron source.
In the field of a field-emission electron source, since development of a semiconductor micro-fabrication technology has enabled the formation of a refined cathode, the technology of vacuum microelectronics has been more and more vigorously developing.
In order to realize a high-performance electron source operable at a lower driving voltage, various attempts have been made to decrease the diameter of the opening of a withdrawn electrode and to manufacture a sharply pointed cathode by utilizing a semiconductor substrate and adopting the LSI technology.
In considering the application of an electron source to a flat display device, it is significant to attain the structure of a vacuum vessel for holding a cathode array portion in a highly vacuum atmosphere capable of electron emission and also to attain a definite vacuum sealing technique.
FIG. 6 is a sectional view of a conventional vacuum-sealed field-emission electron source disclosed in Japanese Laid-Open Patent Publication No. 6-342633. As is shown in FIG. 6, an n-type impurity diffused region 101 is formed in a part of a p-type silicon substrate 100, and on the other part of the p-type silicon substrate 100 not bearing the n-type impurity diffused region 101, plurality of cathodes 102 each in the shape of a spine, together corresponding to a cathode array portion, are formed. Around each of the cathodes 102, a withdrawn electrode 104 is formed with an insulating film 103 disposed therebelow. Each withdrawn electrode 104 is electrically connected with the n-type impurity diffused region 101 through a wire layer 105.
Above the silicon substrate 100, a sealing cover 110 having a recess portion 110a at the center and made from a transparent and insulating material such as glass is provided. A peripheral portion 110b of the sealing cover 110 is positioned substantially at the center of the n-type impurity diffused region 101 of the silicon substrate 100. On the bottom of the recess portion 110a of the sealing cover 110, an anode 111 of a transparent conductive material for converging electrons emitted by the cathodes 102 is disposed. Below the anode 111 is formed a fluorescent thin film not shown.
At the outer side on the n-type impurity diffused region 101 of the silicon substrate 100, an outer electrode connection terminal 106 is provided. The outer electrode connection terminal 106 is electrically connected with the wire layer 105 through the n-type impurity diffused region 101.
In this conventional vacuum-sealed field-emission electron source, the withdrawn electrode 104 is electrically connected with the external electrode connection terminal 106 through the wire layer 105 and the n-type impurity diffused region 101 formed in the silicon substrate 100. Therefore, there is no need to form a wire layer on a portion of the silicon substrate 100 opposing the peripheral portion 110b of the sealing cover 110. As a result, no step is formed by a wire on the portion of the silicon substrate 100 opposing the peripheral portion 110b of the sealing cover 110. Accordingly, this field-emission electron source is good at airtightness between the silicon substrate 100 and the sealing cover 110.
In the vacuum-sealed field-emission electron source, under application of a bias voltage of, for example, approximately 60 V to the withdrawn electrode 104, a control voltage of approximately .+-.10 V is applied to the withdrawn electrode 104, so as to control the on/off operation of the electron emission from the cathodes 102. Specifically, it is necessary to apply the control voltages generally having a potential difference of several tens volts, for example, approximately 20 V, to the withdrawn electrode 104. Also, there is a pn junction in the interface between the p-type silicon substrate 100 and the n-type impurity diffused region 101, and the pn junction has a stray capacitance depending upon a junction capacitance. In order to electrically connect the external electrode connection terminal 106 with the wire layer 105 through the n-type impurity diffused region 101, the area of the n-type impurity diffused region 101 is unavoidably enlarged, resulting in increasing the stray capacitance of the pn junction.
As power consumption is in proportion to a product of an applied control voltage and a stray capacitance, in order to control the on/off operation of the electron emission from the cathodes 102, the power consumption is unavoidably increased for the aforementioned reason.
Furthermore, when an impurity is ununiformly diffused in forming the n-type impurity diffused region 101, a junction defect is caused in the pn junction under application of a high voltage. Therefore, the characteristic of the resultant field-emission electron source can be disadvantageously degraded in its reliability.
Moreover, in the conventional vacuum-sealed field-emission electron source, it is necessary to converge the electrons emitted by the cathodes 102 onto the anode 111 through the fluorescent thin film under application of a voltage of 100 V or more to the anode 111. However, when the field-emission electron source is to be applied to a small and refined display panel, in view of the pitch between wire layers, it is very difficult to take the electrons converged onto the anode 111 out of the sealing cover 110 through the wire layers. This problem will now be described in detail.
FIG. 7 shows a circuit configuration for line control in a matrix display panel. In FIG. 7, a reference numeral 130 denotes the matrix display panel, a reference numeral 131 denotes an X line controller for controlling lines in the X direction, a reference numeral 132 denotes a Y line controller for controlling lines in the Y direction, X.sub.1, X.sub.2, X.sub.3, . . . and X.sub.n respectively indicate wires extending in the X direction controlled by the X line controller 131, and Y.sub.1, Y.sub.2, Y.sub.3, . . . and Y.sub.n respectively indicate wires extending in the Y direction controlled by the Y line controller 132.
For example, in the case of realizing a display of the VGA standard with a panel size of 1 inch or less, the pitches between the wires in the X direction and between those in the Y direction are both 30 .mu.m or less, and hence, a very refined wiring technique is required. According to the current semiconductor processing technology, it is possible to form wires with such a refined pitch on a flat plane but is difficult to form them on a solid structure. Accordingly, in the aforementioned conventional vacuum-sealed field-emission electron source, it is difficult to form the wires with a refined pitch extending from the anode 111 so as to extend windingly along the bottom and the side face of the recess portion 110a of the sealing cover 110 and to pass between the n-type impurity diffused regions 101. Also, the switching operation of the anode 111 requires anode wires in plural layers, but it is very difficult to form the plural wire layers along the bottom and the side face of the recess 110a of the sealing cover 110.
Although it is possible to consider a special wire configuration, for example, in which the sealing cover 110 is provided with through holes for the connection of the wires extending from the anode 111 with the outside of the sealing cover 110, other problems such as an increased number of manufacturing procedures and an increased manufacturing cost can occur when such a special configuration is adopted.